http://197.159.135.214/jspui/handle/123456789/8 2026-06-25T07:13:27Z 2026-06-25T07:13:27Z Sitta, Aissatou http://197.159.135.214/jspui/handle/123456789/1251 2026-06-24T15:19:35Z 2025-06-01T00:00:00Z

Operational Seasonal Climate Forecast Methods and Skills over the Sahelian Region of West Africa Sitta, Aissatou In the context of increasing climate change and variability, reliable climate seasonal forecasts play critical role in agricultural planning. Recurring droughts, erratic rainfall, and limited adaptive capacity in the Sahel have highlighted the need for timely and usable climate information to enhance resilience among smallholder farmers. The West African Regional Climate Outlook Forums (WARCOF or PRESASS in French) forecasting system, predicts annually the rainy season key parameters (season cumulative rainfall, onset date, cessation date and length of dry spells). The WARCOF often shows significant percentage of forecast mismatches with observation. Thus, it urges to evaluate the performance and practical relevance of the WARCOF/PRESASS approach that has been used since 2011. The research aimed to assess the technical skill of the forecasting system, identify pathways to improve prediction accuracy, and examine how farmers access and utilize forecast information. Specifically, it was achieved through: first by the evaluation of the forecast skills for onset, cessation, and dry spells; then by the research on alternative predictors and statistical methods for forecast enhancement; and finally by the investigation on the dissemination and adoption of forecasts information among smallholders farmers. The guiding research question was: how can seasonal climate forecasts be improved and effectively communicated to strengthen smallholders’ adaptive strategies in West Africa? A mixed-methods approach was adopted. Quantitative forecast verification techniques (such as reliability diagrams, ROC curves, and Brier scores) were used to analyze historical forecasts against observed data from 1991 to 2023. The Climate Predictability Tool (CPT) was applied for statistical modelling using sea surface temperature (SST) anomalies, precipitation hindcasts, and newly tested predictors like April-May-June (AMJ) cumulativerainfall and wet-day frequencies. Additionally, qualitative data obtained from a baseline survey of 619 farmers and quantitative data from two-year demonstration trials in four municipalities of southwest Niger were used. Key findings indicate that in the WARCOF/PRESASS approach, onset forecasts demonstrated higher skill and reliability compared to cessation and dry spells, particularly when using precipitation hindcasts (e.g., NASA and CFSv2) as predictors. Incorporating wet-days and AMJ rainfall totals as alternative predictors significantly improved forecast skill. However, dry spell forecasts exhibited low discrimination ability. The field-level study revealed that only 42.3% of farmers had access to forecasts, and those who fully applied the information achieved measurable yield gains (up to 234 kg/ha) compared to traditional practices, validating the forecast's real-world utility. The positive impact of the forecast information on yield was more noticeable in drought prone areas (trials sites in Sahelian and Sudano-Sahelian zones) compared to wetter areas in the Sudanian zone; showing the relevance of climate information dissemination in the most vulnerable area. The study concludes that enhancing the PRESASS forecasting system requires scientific recalibration using high-performing predictors and user-oriented communication strategies. Co-production of forecasts, capacity building, and integration with local agricultural calendars are essential to maximize uptake and effectiveness. The findings contribute to climate resilience strategies and support SDGs 1 (No Poverty), 2 (Zero Hunger), and 13 (Climate Action), as well as WASCAL's priorities on sustainable agriculture and climate risk reduction. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Federal University of Technology, Akure, Nigeria, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in West African Climate Systems

2025-06-01T00:00:00Z Odoulami, Romaric Christel http://197.159.135.214/jspui/handle/123456789/1250 2026-06-24T14:48:35Z 2016-06-01T00:00:00Z

Modelling the Potential Impacts of Forestation on Extreme Climate Events over West Africa Odoulami, Romaric Christel Previous studies on climate change projections over West Africa did not include the influence of on-going forestation activities on future climate extremes over the region. The present study aimed to examine the potential impacts of a large scale forestation activity on the future characteristics of extreme climate events (extreme rainfall and heatwaves) over West Africa using Regional Climate Models (RCMs). The specific objectives of the study were to: (i) examine RCMs ability to simulate extreme climate events over West Africa; (ii) investigate the potential impacts of climate and forestation on extreme rainfall events over West Africa; and (iii) examine the potential impacts of climate and forestation on heatwaves characteristics over West Africa. The study applied two RCMs (RegCM and WRF) to simulate the present day (PRS, 1970-2004) and the future (2030-2064) climates, with and without forestation (GHG and FRS, respectively). The simulations account for the potential impacts of forestation over the Savannah zone (8°N - 12°N) in West Africa. In this study, an extreme rainfall event is said to occur when the daily rainfall amount exceeds a threshold value (i.e. 95th percentile of the daily rainfall) and a Widespread Extreme Rainfall Event (WERE) is defined as the simultaneous occurrence of extreme rainfall that covers at least 50% of a given area. Heatwaves are identified using two metrics: the excess heat factor (EHF) and a percentile based index (TXI: 90th percentile of daily maximum temperature). The RCMs ability to simulate the characteristics of extreme events for PRS is assessed against observed datasets: the Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measurement Mission (TRMM) for extreme rainfall events analysis; and the Princeton University Global Meteorological Forcing Dataset (PGFD) for heatwaves analysis. The results show that both RCMs reproduce well the extreme rainfall threshold values (95th percentile) over West Africa and WEREs over Savannah in comparison with the observation datasets (GPCP and TRMM), though with some notable discrepancies. The RCMs generally overestimate the threshold of extreme rainfall over coastal areas and highlands, and simulated WEREs earlier than observed. For heatwaves, the two methods (EHF and TXI) generally produce similar patterns of heatwave characteristics over West Africa, except that heatwave number and days are substantially greater with TXI than with EHF. Also, the models give a realistic simulation of extreme temperature thresholds and heatwave characteristics over West Africa, although with some apparent biases. The results agree with previous studies that the Representative Concentration Pathway (RCP4.5) emission scenario would increase the frequency and intensity of extreme climate events over West Africa in future. In fact climate change would increase the frequency of extreme rainfall events over parts of the Guinea coast (and lower it over the Sahel zone), and heatwave number, days and duration over the whole region in future. The results further indicate that forestation would enhance the characteristics of extreme events over West Africa in future. Forestation generally increases the frequency and intensity of extreme rainfall events over the forested zone and decreases it elsewhere. Also, both models suggest that forestation would increase WERE frequency in parts of the Savannah zone. Similarly, forestation would also increase heatwave number and days over the forested area as the forestation would decrease surface albedo which during the dry season would increase the net solar radiation making more energy available at the surface. The outcomes of the present study suggest that the use of forestation to mitigate the impacts of climate change over West Africa might induce undesirable climatic impacts (increase in extreme rainfall and heatwave events) over some locations of the subcontinent, thereby increasing the climatic risk on human health and security. Therefore, the results of this study may guide decision makers in improving the resilience of West African countries to the consequences of climate and weather extremes and also in choosing appropriate climate change mitigation and adaptation options. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Federal University of Technology, Akure, Nigeria, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in West African Climate Systems

2016-06-01T00:00:00Z Faye, Aissatou http://197.159.135.214/jspui/handle/123456789/1249 2026-06-24T14:19:40Z 2019-10-01T00:00:00Z

Modelling the Impact of Coastal Urbanization on the West African Summer Monsoon Climate Faye, Aissatou A lot of research has been done to understand and improve the relationship between land use and land cover modification vis-a-vis their interaction with the West African climate variability and climate change. However, the urbanization influence on the West African climate is not yet an elaborately researched subject of studies. In this context, this thesis examines the impact of coastal urbanization on the West African summer climate, by using the Regional Climate Model version 4 (RegCM4) coupled with the Community Land Surface Model version 4.5 (CLM4.5). A series of experiments were performed, in the present-day climate (1984-2005) and the RCP8.5 far future (2079- 2100), at 25 Km of horizontal resolution over the West African domain. Two types of simulations were performed with and without modification of the natural vegetation land cover with the urban parameterization (CLMU). Results from the model evaluation show the good performance of RegCM4 to simulate the main climatic variables and atmospheric circulation over West Africa during the June-September (JJAS) summer months. Arguably, RegCM4 reproduces well the spatio-temporal pattern of rainfall and temperature over West Africa in comparison with observations datasets. Again, the model’s capability to reproduce the West African atmospheric circulation drives and atmospheric variables compared to reanalyses was examined. RegCM4 gives a good representation of atmospheric circulation from the lower to the upper troposphere. The projected changes in West African climate under RCP8.5 and both RCP8.5 and urbanization were evaluated. For all the simulations, a significant warming is expected over the whole West Africa and will be more pronounced in the Sahel-Sahara at the end of the 21st century. A significant increase in temperature is also expected along the West African coastal region which corresponded to the ‘perturbed’ region. In the precipitation simulations, all the different simulations projected drier conditions in visually the entire West African region. However, the expected change is less significant in the combined urban expansion and RCP8.5 simulations. Evaluation of contribution due to urbanization alone shows that the change in the land cover gave a response of an average increase in temperature of approximately 3ºC over the urbanized region. The results imply that urban effects can reach the same magnitude as global warming. This warming could be a result of the urban heat island processes. Precipitation in the urbanized region and their sub-urban regions shows an increase of at least ~10%. This means that urbanization has both local and regional effects on the precipitation in West Africa. Furthermore, the results show that the characteristics of some atmospheric circulation such as AEJ and AEWs would change in the future climate. For example, a southward displacement of the AEJ position was observed which can explain the projected drier conditions in the region, especially in the Sahel part. Moreover, it should be noted that urbanization influences the atmospheric circulation drivers through the AEJ and AEWs. More convective activities are found under urban conditions and the sensitivity of the AWEs to the land surface conditions is noticed. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Federal University of Technology, Akure, Nigeria, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in West African Climate Systems

2019-10-01T00:00:00Z Gbode, Imole Ezekiel http://197.159.135.214/jspui/handle/123456789/1248 2026-06-24T14:12:14Z 2019-09-01T00:00:00Z

Evaluation of Weather Research and Forecasting Model Physics in Simulating West African Monsoon Gbode, Imole Ezekiel This research evaluates the ability of Weather Research and Forecasting model physics in simulating the West African monsoon. The purpose is to identify a possible model physics combinations in the WRF model whose outputs can be used to inform weather- and climate-related decision-making process at local to regional scale. In the study, the sensitivity of West African Monsoon (WAM) regimes to three model physics (i.e. Cumulus (CU), Microphysics (MP) and Planetary Boundary Layer (PBL) parameterization schemes) is assessed, performance of the model in representing the WAM dynamics is evaluated and impact of warming climate on WAM under the RCP8.5 scenario is also assessed. Twenty-seven (27) WRF simulations of the August-September 2007 monsoon regime at a 20-km grid over West Africa were evaluated to investigate the sensitivity of the WAM regime to the three model physics. The focus was on precipitation and surface temperature during the simulated period. The model’s precipitation was evaluated against the TRMM (reference), CMORPH and GPCP satellite rainfall products. Also, the surface temperature was evaluated against the ERA-Interim (reference), NCEP, MERRA, and GSAT. Results showed that all model physics combinations simulated the diurnal cycles of surface temperature better than the simulation of precipitation. A comparative model skill score was developed and used to identify that combination of WSM5-MYNN-nTDK and GD-MYJ-BMJ are best performing physics combinations in both temperature and precipitation. Also, the three WRF model physics combinations reproduced the characteristics of the region’s monsoon during selected normal (2007), wet (2008 and 2010) and dry (2001 and 2011) years. The dynamics of WAM such as monsoon flow, African Easterly Jet, and Tropical Easterly Jet, are replicated by most of the model combinations. Therefore, underscoring the strong potential impact of regional moisture, heat and momentum transport and redistribution on the monsoon dynamics as prescribed by the physics. Lastly, the Pseudo-Global Warming (PGW) simulation method perturbed by CESM1.0-CAM5.2 is employed to assess the impact of warming on WAM, the result shows a slight increase in precipitation amount (-2 to 16%) in the 2070s when compared with the current (reference) climate. This change is expected to be more pronounced in the Sahel, where the value is 16%, and less than 3% in the Guinea Coast. Furthermore, there is a decrease (increase) in both light and moderate (heavy) rainfall days. The outcomes of this research underscore the significance of WRF model as a potentially useful tool to investigate how future WAM seasons could vary in a changing climate. This provides relevant information to improve the understanding of the possible implications of such changes on economic activities such as agriculture, water resources, and other climate-related sectors, and to guide the design and implementation of climateresilient projects. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Federal University of Technology, Akure, Nigeria, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in West African Climate Systems

2019-09-01T00:00:00Z